Fullscreen QML Window on OSX

I am developing a QML application. The main file is a QtObject with a splash screen (Window) in it. While the splash screen is visible, I use a Loader to asynchronously load the main window (Window). I set the visible flag of the Loader to false until loading is completed, and then I want to hide the splash screen and show the main window fullscreen.

The problem is that I cannot get the main window to properly display in fullscreen mode on OSX. When setting the visibility to Window.FullScreen the window maximizes and the OSX menu bar is hidden. The window does not take the place of the now empty bottom though, and the top window bar is still displayed.

I tried to explicitly set the flags of the window to Qt.Window | Qt.WindowFullScreenButtonHint but no fullscreen button is shown, only maximize.

This used to work properly when the main window was the top item, before I used the splash screen. It still works correctly on windows.

Am I doing something wrong or is this a bug? I am using both Qt 5.6.1 and 5.7 with the same results.